Multiple-input multiple-output (MIMO) technology implemented at a large scale is a key to 5th generation (5G) wireless networks. Using a so-called massive MIMO antenna, a 5G base station is able to form spatially separated narrow beams, each pointing to different user equipment (UE) such as wireless mobile devices at different respective locations. The massive MIMO antenna is a base station antenna with numerous antenna elements that can be dynamically grouped in subsets to each form and radiate a narrow beam. The narrow beam radiated from each different subset of antenna elements can be radiated directionally in a primary direction different from narrow beams radiated from other subsets of antenna elements. The massive MIMO antenna that simultaneously radiates narrow beams in different directions enlarges network capacity, improves spectrum efficiency, and enables simultaneous access by different user equipment in spatially diverse locations. However, to benefit from the massive MIMO antenna and spatially separated narrow beams, the base station and the user equipment should have a mechanism to find an optimized beam for communicating between the base station and the user equipment, and to control the beam to continuously track movement of the user equipment. The user equipment designed and optimized for 5G networks also needs to be tested for interoperability with the 5G base stations. Test solutions which can test end-to-end performance of the user equipment communicating with a 5G base station (i.e., using a massive MIMO antenna) are thus needed.
With the evolution of wireless communications technologies, user equipment increasingly has antennas that are directly connected to and integrated with radio frequency (RF) transceivers, and thus are increasingly provided with no RF connectors. Overall performance of such user equipment as a device under test (DUT) being tested by a testing system presently must be tested over-the-air (OTA) since there is no place (e.g., no RF connector) to connect a coaxial cable from the user equipment and/or the antenna to test equipment. In fact, due to antenna integration, overall user equipment performance is now typically tested as a function of the antenna configuration.
To characterize performance, various attributes of the user equipment, such as radiation profile, effective isotropic radiated power, total radiated power, error-vector-magnitude (EVM) of the modulation, and adjacent channel leakage ratios (ACLRs), for example, are characterized as a function of beam angle. This may involve a time-consuming process. For example, characterizing just the radiation profiles of the user equipment as a function of beam angle may take hours.
Conventional solutions for testing user equipment performance in wireless networks may suffer from a variety of shortcomings in communications with base stations using dynamic beamforming, such as in 5G networks. For example, one such conventional solution is a multiple probe anechoic chamber (MPAC) based MIMO OTA test system which includes a base station emulator. Anechoic chambers are shielded, including walls covered in absorbing material that minimizes internal reflections, typically by several tens of decibels. The MPAC-based MIMO OTA test system is designed to test the user equipment downlink MIMO OTA performance. However, the MPAC-based MIMO OTA test system does not provide for user equipment uplink spatial channel emulation. Additionally, the MPAC-based MIMO OTA test system does not include the 5G base station (i.e., with the massive MIMO antenna), due for example to the large number of channels used by the 5G base station. The MPAC-based MIMO OTA test system is also not designed to support channel emulation for the 5G base station described above. Insofar as a narrow beam will make a channel much more directional at the user equipment side, a ring of measurement probes in the MPAC may not even adequately support the bi-direction spatial channel emulation. Moreover, the base station emulator used in the MPAC-based MIMO OTA test system typically does not work with fading uplink channels. Therefore, an MPAC-based MIMO OTA test system is not particularly suitable for testing user equipment performance in 5G networks.
Another conventional testing solution for testing user equipment is the radiated two-stage (RTS) method. The RTS system is designed to test the user equipment downlink MIMO OTA performance but suffers from several of the same shortcomings as the MPAC-based MIMO OTA test system described above. For example, the RTS system does not include the user equipment uplink spatial channel emulation. Additionally, the RTS system does not include a base station that uses a massive MIMO antenna for end-to-end test. Moreover, the base station emulator used in the RTS system typically does not work with fading uplink channels.
Other conventional testing solutions do not test the user equipment antenna, or do not test radiation performance of the user equipment as the DUT at all. Even testing performance of the user equipment as the DUT in the field in a real network is not particularly suitable, insofar as testing in a real network may provide for overall network quality evaluation but does not provide for a controllable and repeatable test environment for testing performance of the user equipment and the user equipment antenna.
Therefore, a practical approach is needed for testing performance of the user equipment communicating with base stations using dynamic beamforming, such as in 5G networks.